The present invention generally pertains to antenna systems and is particularly directed to antenna systems for use in missile guidance systems.
An antenna system which is used for tracking targets is included in a guidance system of a missile which is intended to seek out and destroy electromagnetic radiation sources, such as enemy search and guidance control radar systems. In order to counteract the threat of early shutdown of target radiation sources, future generation antiradiation missiles must be equipped with more highly accurate seeker antenna systems for tracking target radiation sources. This implies a need for a significant reduction (by approximately an order of magnitude) in the boresight error of the antenna system and also a significant reduction in the radome error slope.
In a typical antiradiaton missile, a seeker antenna system is positioned within the radome at the nose of the missile. The seeker antenna system is used to detect a radiation source, whereupon the guidance system responds to such detection by causing the missile to home in on the radiation source. In one type of antiradiation missile guidance system, the seeker antenna system is a planar multi-arm spiral antenna which is gimballed for movement throughout a conical angle within the radome. The radiation field covered by the antenna is ahead of the missile and centered about the boresight axis of the missile. The angular deviation of the electrical boresight of an antenna from its reference boresight is known as boresight error. A significant factor contributing to boresight error is the presence of the radome, since wavefronts passing through the radome to the antenna are somewhat distorted. The radome error slope is the variation in boresight error as a function of the look angle of the antenna through the radome.
It is a principal object of the present invention to provide a monopulse antenna system for use in a missile guidance system, wherein the boresight error and the radome error slope of the antenna system are significantly reduced.